1. Field of the Invention
The present invention relates to an organic monomolecular thin-film manufacturing method for manufacturing an organic monomolecular film arranged two-dimensionally on an Si substrate.
2. Description of the Prior Art
Conventional organic monomolecular films include Langmuir Blodgett films (hereafter referred to as "LB films") and self-assembled monolayers (Abraham Ulman: An Introduction to Ultrathin Organic Films From Langmuir-Blodgett to Self-Assembly, Academic Press 1991).
An LB film is formed by developing on a water surface, as a monomolecular film, amphipathic molecules including hydrophilic groups and hydrophobic groups (an L film). The film is transferred onto a solid substrate, and several such films are accumulated thereon, according to the process named after Langmuir and Blodgett. A self-assembled monolayer is obtained by allowing the functional groups at the terminals of molecules to be chemically adsorbed by the atoms constituting the substrate. This film is called the "self-assembled monolayer" because, due to the relevant adsorption mechanism, only monomolecular films are self-organized and formed on the substrate.
Films can also be accumulated by selecting the type of the terminal group outside a formed self-assembled monolayer. These monomolecular films form a two-dimensional monomolecular aggregate due to the Van der Waals force of the molecules, and these methods can be used to manufacture a regular arrangement of molecular packings, that is, two-dimensional crystals. This feature can be used to construct electronic and optical devices.
Since an LB film is formed by transferring a film developed on the water surface, onto the substrate, using the difference between the hydrophobic and hydrophilic properties of the film and the substrate, the crystallinity of the film is determined when the film is expanded and compressed. Thus, the crystallinity of the film does not depend on the type of the substrate, and the film can be formed on any substrate. The interaction between the substrate and the monomolecular film, however, is very weak due to the nature of the LB film, and the film lacks the acid- and alkali-resistance and durability required to construct complicated devices.
On the other hand, the self-assembled monolayer does not have the above disadvantages, but due to the use of the chemical adsorption between the functional groups of molecules and the substrate, their range of combinations is limited. Monomolecular films have thus been implemented on substrates of silicon oxide, aluminum oxide, silver oxide, mica, gold, copper, or GaAs. For silicon substrates, only self-assembled monolayers using the covalent bonding between a silicon oxide film and SiCl.sub.8 group have been obtained.
Since, however, the self-assembled monolayer uses the chemical reaction between an amorphous oxide film and SiCl.sub.8 groups on silicon, the crystallinity of a self-assembled monolayer obtained has been very poor, that is, the quality of this film has been lower than that of the LB film. The film quality directly relates to quantum efficiency that provides a functionality characteristic of that monomolecular film, and thus contributes to producing substantial adverse effects in manufacturing devices.